Transferring and fixing the final image with heat is widely standard in electrophotographic apparatus. In U.S. Pat. No. 5,291,225 to Britto et al, Ser. No. 07/945,195, filed Sept. 15, 1992, heating is in two stages, the final stage being the paper pressed between a member carrying the image and a heated transfer roller. Immediately preceding that stage is a heated, flat plate on which the image receiving surface of the paper is pressed prior to the transfer at the final stage. The path over the plate and to the nip of the final stage is straight.
The foregoing patent to Britto et al is assigned to the same assignee to which this invention is assigned. This invention preferably employs those two stages and the straight-path for transfer. This invention also employs a prior stage in which the paper is thoroughly dried under heat and immobilizing pressure prior to moving over the heated plate. This dries and apparently otherwise conditions the paper to achieve excellent, consistent results with a wide range of papers.
In the Britto et al apparatus the transfer location has a relatively small second transfer roller, and that roller could be heated sufficiently high to effect transfer without unduly heating the larger, first transfer roller or being so hot as to cause fumes or emissions. In this invention, a large transfer roller may be one of the two rollers at the transfer location.
U.S. Pat. No. 5,204,722 to Thompson et al preheats the paper on a flat plate and mentions a purpose of driving "out excess moisture from the paper, particularly on the side to which the toner is to be transferred."Such heating is not the preheating under immobilizing pressure of this invention.